Erik Miranda

Hyperspectral Modeling of Skin Appearance

Exploration of the hyperspectral domain offers a host of new research and application possibilities involving material appearance modeling. In this article, we address these prospects with respect to human skin, one of the most ubiquitous materials portrayed in synthetic imaging. We present the first hyperspectral model designed for the predictive rendering of skin appearance attributes in the ultraviolet, visible, and infrared domains. The proposed model incorporates the intrinsic bio-optical properties of human skin affecting light transport in these spectral regions, including the particle nature and distribution patterns of the main light attenuation agents found within the cutaneous tissues. Accordingly, it accounts for phenomena that significantly affect skin spectral signatures, both within and outside the visible domain, such as detour and sieve effects, that are overlooked by existing skin appearance models. Using a first-principles approach, the proposed model computes the surface and subsurface scattering components of skin reflectance taking into account not only the wavelength and the illumination geometry, but also the positional dependence of the reflected light. Hence, the spectral and spatial distributions of light interacting with human skin can be comprehensively represented in terms of hyperspectral reflectance and BSSRDF, respectively.

On the noninvasive optical monitoring and differentiation of methemoglobinemia and sulfhemoglobinemia

Abstract. There are several pathologies whose study and diagnosis is impaired by a relatively small number of documented cases. A practical approach to overcome this obstacle and advance the research in this area consists in employing computer simulations to perform controlled in silico experiments. The results of these experiments, in turn, may be incorporated in the design of differential protocols for these pathologies. Accordingly, in this paper, we investigate the spectral responses of human skin affected by the presence of abnormal amounts of two dysfunctional hemoglobins, methemoglobin and sulfhemoglobin, which are associated with two life-threatening medical conditions, methemoglobinemia and sulfhemoglobinemia, respectively. We analyze the results of our in silico experiments and discuss their potential applications to the development of more effective noninvasive monitoring and differentiation procedures for these medical conditions.

Spectral appearance changes induced by light exposure

The fading of materials due to light exposure over time is a major contributor to the overall aged appearance of man-made objects. Although much attention has been devoted to the modeling of aging and weathering phenomena over the last decade, comparatively little attention has been paid to fading effects. In this article, we present a theoretical framework for the physically based simulation of time-dependent spectral changes induced by absorbed radiation. This framework relies on the general volumetric radiative transfer theory, and it employs a physicochemical approach to account for variations in the absorptive properties of colorants. Employing this framework, a layered fading model that can be readily integrated into existing rendering systems is developed using the Kubelka-Munk theory. We evaluate its correctness through comparisons of measured and simulated fading results. Finally, we demonstrate the effectiveness of this model through renderings depicting typical fading scenarios.

Effects of sand grain shape on the spectral signature of sandy landscapes in the visible domain

In this paper, we investigate the effects of sand grain shape on the reflectance of sandy landscapes within the visible domain. Our investigation is supported by computer simulations performed using SPLITS (Spectral Light TransportModel for Sand) and taking into account actual sand characterization data. Our findings indicate that the spectral effects of grain shape may vary considerably depending on the distribution patterns of iron oxides present in sand-textured soils. These patterns and grain shape properties, namely roundness and sphericity, are largely determined by the formation processes of these soils. Hence, we believe that their interplay should be carefully taken into account in the retrieval of information about the mineralogy and morphology of sandy terrains.

Influence of Sand-Grain Morphology and Iron-Oxide Distribution Patterns on the Visible and Near-Infrared Reflectance of Sand-Textured Soils

The overall shape of a sand grain can be defined by two morphological properties, namely sphericity and roundness, and it is largely determined by soil-formation and weathering processes. In this paper, we investigate the effects of these properties on the visible and near-infrared reflectance of sand-textured soils characterized by the presence of iron oxides. Our investigation is supported by computer simulations performed using the SPLITS (Spectral Light Transport Model for Sand) model and considering actual sand characterization data. Our findings indicate that the influence of grain morphology may vary considerably depending on the distribution patterns of iron oxides present in sand-textured soils. These minerals may occur as pure particles, as contaminants mixed with the grain parent material, or as coatings. Since these distribution patterns are also significantly affected by soil-formation and weathering processes, we believe that the combined influence of sand-grain shape and iron-oxide distribution patterns on the reflectance of sandy landscapes should be carefully taken into account in the retrieval of information about their mineralogy and environmental history.

On the high-fidelity monitoring of C3 and C4 crops under nutrient and water stress

The different photosynthetic and morphological characteristics of C3 and C4 plants may lead to distinct physiological responses of C3 and C4 crops to stress factors. These responses are strongly correlated with the red edge of these plants, the s-shaped curve in the 680-800nm region of their reflectance spectra. We performed controlled in silico experiments to investigate the patterns of the red edge displacements resulting from C3 and C4 specimens subjected to the same stress conditions. Our findings indicate these patterns need to be taken into account in the development of effective monitoring procedures for C3 and C4 crops.

Assessing the Spectral Sensitivity of Martian Terrains to Iron Oxide Variations Using the SPLITS Model

The mineralogy and environmental history of Mars are being extensively studied through remote sensing observations paired with laboratory and in situ experiments. A significant portion of these experiments is being devoted to the identification and mapping of different iron oxides present in the Martian terrains. Among these compounds, goethite has been an object of great interest since its occurrence can be interpreted as mineralogical evidence of past aqueous activity on those landscapes. Although such experiments can provide valuable information regarding the presence of these minerals, the scope of the resulting observations may be hindered by logistics and cost-related constraints. We believe that predictive computer simulations can be employed to mitigate some of these constraints and contribute to the generation and validation of hypotheses in this area. Accordingly, we propose the use of SPLITS (Spectral Light Transport Model for Sand) in investigations involving the spectral signatures of iron-bearing regions of Mars. In this paper, we initially demonstrate the predictive capabilities of the SPLITS model in this context through qualitative comparisons of modeled results with actual observations and measured data. Using the resulting modeled reflectance curves as our baseline data, we then perform a series of controlled computational experiments to investigate how variations on goethite and hematite content affect the spectral responses of Martian sand-textured soils.

Simulating the spectral properties of iron-bearing regions of Mars using the SPLITS model

The mineralogy and environmental history of Mars are been extensively investigated through remote sensing observations paired with laboratory and in situ experiments. A significant portion of these experiments is being devoted to the identification and quantification of different iron oxides present in the Martian terrains. Although such experiments can provide valuable information regarding the presence of these minerals, the scope of the resulting observations may be hindered by logistics and cost-related constraints. We believe that predictive computer simulations can be employed to mitigate some of these constraints and contribute to the generation and validation of hypotheses in this area. Accordingly, we propose the use of SPLITS (Spectral Light Transport Model for Sand) in investigations involving the spectral signatures of iron-rich sand-textured soils found on Mars, and demonstrate its predictive capabilities in this context through comparisons of modeled results with actual measured data.

High-fidelity iridal light transport simulations at interactive rates: High-fidelity iridal light transport simulations at interactive rates

Predictive light transport models based on first‐principles simulation approaches have been proposed for complex organic materials. The driving force behind these efforts has been the high‐fidelity reproduction of material appearance attributes without one having to rely on the manipulation of ad hoc parameters. These models, however, are usually considered excessively time consuming for rendering and visualization applications requiring interactive rates. In this paper, we propose a strategy to address this open problem with respect to one of the most challenging of these organic materials, namely the human iris. More specifically, starting with the configuration of a predictive iridal light transport model on a parallel‐computing platform, we analyze the sensitivity of iridal appearance attributes to key model running parameters in order to achieve an optimal balance between fidelity and performance. We believe that the proposed strategy represents a step toward the real‐time and predictive synthesis of high‐fidelity iridal images for rendering and visualization applications, and it can be extended to other organic materials.